Hematophagous flies are a pest for livestock; their direct impact reduces productivity, and they are vectors of parasites, bacteria and viruses. Their control using insecticides is inefficient and highly polluting. The validation of new control tools requires efficacy and cost-effectiveness evaluation. The quantification of hematophagous insects' impact in livestock is a challenging prerequisite. Tail flicks counts can reliably evaluate fly-burden; however, visual records are tedious and time-consuming. In the present study, automation of tail flick counts was made through the use of pedometers attached to the tail, in two groups of feeder cattle. Group A was kept in a pen under the protection of a mosquito net, and Group B was kept in an open-air pen. The fly density of Group B was evaluated using fly traps. The apparent density per trap ranged from 130 to 1700 in the study. The mean pedometer records per 24 h ranged from 957+/-58 bits in Group A to 11,138+/-705 bits in Group B. The night/day records observed in Group A (200/800 bits) were drastically increased in Group B (1000–4000/4000–14,000 bits) and variable along seasons. A very high correlation was observed between fly density and visual records or pedometer records (PR). Two-hour PRs proved to be a reliable predictive tool for fly density. Moreover, the pedometers revealed an unsuspected but significant nuisance of mosquitoes, which should be thoroughly investigated.